Battery

ABSTRACT

A battery is provided in the present disclosure. The battery includes: a positive electrode plate including a positive current collector and a positive active material layer; a negative electrode plate including a positive current collector and a negative active material layer; and an electrolyte. The positive current collector includes an insulation layer used to support a conductive layer and the conductive layer used to support the positive active material layer and located above at least one surface of the insulation layer. The conductive layer has a thickness of D2 which satisfies: 300 nm≤D2≤2 μm. A protective layer is arranged on at least one surface of the conductive layer. The negative current collector is a copper foil current collector having a thickness of 1 μm to 5.9 μm.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. applicationSer. No. 16/161,978, filed on Oct. 16, 2018, which claims priority toChinese Patent Application No. 201711268374.1, filed on Dec. 5, 2017,the content of which is incorporated herein by reference in itsentirety; and the present application also claims priority to ChinesePatent Application No. 201910345708.3, filed on Apr. 26, 2019, thecontent of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to the field of batteries and,particularly, relates to a battery.

BACKGROUND

Lithium ion batteries have been widely used in electric vehicles andconsumer electronics due to their advantages such as high energydensity, high output power, long cycle life, and low environmentalpollution. However, when the lithium ion batteries are subjected toabnormal conditions such as extrusion, collision, or puncture, they caneasily to catch fire or explode, causing serious problems. Therefore,the safety issue of the lithium ion batteries greatly limits theapplication and popularization of the lithium ion batteries.

A large number of experimental results show that an internal shortcircuit in a battery is the ultimate cause of safety hazards of thelithium ion batteries. In order to avoid the internal short circuit inthe battery, researchers tried to improve the separator structure,battery mechanical structure and so on. Some of these studies haveimproved the safety performance of the lithium ion batteries bymodifying the design of current collectors.

The temperature in the battery may rise when an internal short circuitoccurs in the battery due to abnormal conditions such as collision,extrusion, or puncture and on the like. According to a technicalsolution in the related art, there is a technical solution in whichalloy having a low melting point is added into the material of a metalcurrent collector. With increasing of the temperature of the battery,the alloy having low-melting point in the current collector begins tomelt, thereby resulting in a broken circuit of an electrode plate andcutting off the current. In this way, the safety of the battery isimproved. According to another technical solution in the prior art, amultilayered current collector is adopted, in which both sides of aresin layer are connected with metal layers to form a composite. Whenthe temperature of the battery reaches a melting point of the materialof the resin layer, the resin layer of the current collector melts todamage the electrode plate, thereby cutting off the current andenhancing the safety of the battery.

However, these solutions in the related art cannot effectively preventthe occurrence of the internal short circuit in the lithium ion battery,and cannot guarantee that the battery can continue to operate under theabnormal conditions. In the above solutions, the temperature in thebattery would still rise sharply after the internal short circuit occursin the battery. When the battery temperature rises sharply, danger ofvarying degrees would still occur if the safety component cannot respondquickly. In these solutions, even the safety component responds andsuccessfully avoids the hazard of the battery, the battery cannotcontinue to operate.

Therefore, it is necessary to provide a design of a battery that caneffectively prevent accidents such as firing and explosion caused by theoccurrence of the internal short circuit under the abnormal conditionssuch as collision, extrusion, or puncture, without affecting the normaloperation of the battery.

SUMMARY

The present disclosure provides a battery, which can improve safetyperformance while having good rate performance.

In a first aspect of the present disclosure, a battery is provided. Thebattery includes a positive electrode plate, a negative electrode plateand an electrolyte. The positive electrode plate includes a positivecurrent collector and a positive active material layer. The negativeelectrode plate includes a negative current collector and a negativeactive material layer, and an electrolyte. The positive currentcollector includes an insulation layer and at least one conductivelayer. The insulation layer is used to support the at least oneconductive layer. Each of the at least one conductive layer is used tosupport the positive active material layer and is located above at leastone surface of the insulation layer. Each of the at least one conductivelayer has a thickness of D2 satisfying: 300 nm≤D2≤2 μm. At least oneprotective layer is arranged on at least one surface of each of the atleast one conductive layer. The negative current collector is a copperfoil current collector having a thickness of 1 μm to 5.9 μm.

The technical solution of the present disclosure has at least thefollowing beneficial effects.

Firstly, the insulation layer of the positive current collector in thebattery of the present disclosure is non-conductive, so its resistanceis large. This can improve the short circuit resistance of the batterywhen the short circuit occurs under abnormal conditions, such that theshort circuit current can be greatly reduced, and thus the heatgenerated by the short circuit can be greatly reduced, thereby improvingthe safety performance of the battery. Meanwhile, the weight energydensity of the battery can be increased by replacing the conventionalcurrent collector of metal foil with an insulation layer provided with aconductive layer having a smaller thickness.

Secondly, a protective layer is further arranged above the positivecurrent collector in the battery of the present disclosure. On one hand,the conductive layer can ensure that the current collector can provideelectrons to the electrode active material layer, that is, it has theeffects of conduction and current collection. On the other hand, theprotective layer can further improve the overall mechanical strength ofthe current collector, further improve the safety performance of thebattery, and at the same time effectively prevent the conductive layerfrom being damaged, oxidized or corroded, etc., and thus significantlyimprove an operating stability and a service life of the currentcollector.

Finally, although the positive current collector of the batteryaccording to the present disclosure can improve the safety performanceof the battery, its conductivity is inferior to that of the conventionalcurrent collector of aluminum foil. Therefore, the present disclosureuses a copper foil current collector having a thickness of 1 μm to 5.9μm as the negative current collector of the battery. Therefore, the rateperformance of the battery can be ensured and the negative electrode canbe prevented from precipitating lithium.

The battery in the present disclosure can not only improve the safetyperformance of the battery, but also have the good rate performance, andcan also improve the weight energy density of the battery.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a structural schematic diagram of a positive current collectoraccording to an embodiment of the present disclosure;

FIG. 2 is a structural schematic diagram of a positive current collectoraccording to another embodiment of the present disclosure;

FIG. 3 is a structural schematic diagram of a positive current collectoraccording to another embodiment of the present disclosure;

FIG. 4 is a structural schematic diagram of a positive current collectoraccording to another embodiment of the present disclosure;

FIG. 5 is a structural schematic diagram of a positive electrode plateaccording to an embodiment of the present disclosure;

FIG. 6 is a structural schematic diagram of a positive electrode plateaccording to another embodiment of the present disclosure;

FIG. 7 is a schematic diagram showing a one-time nailing experiment ofthe present disclosure;

FIG. 8 is a schematic graph of temperatures of Battery 1 and Battery 4after the one-time nailing experiment;

FIG. 9 is a schematic graph of voltages of Battery 1 and Battery 4 afterthe one-time nailing experiment;

FIG. 10 is a sectional view showing cutting of a negative electrodeplate according to an embodiment of the present disclosure;

in which:

-   -   1—positive electrode plate;    -   10—positive current collector;    -   101—positive insulation layer;    -   102—positive conductive layer;    -   103—positive protective layer;    -   11—positive active material layer;    -   2—negative electrode plate;    -   20—negative current collector;    -   21—negative active material layer;    -   3—separator;    -   4—nail.

DESCRIPTION OF EMBODIMENTS

Hereafter, the present disclosure will be further described incombination with specific embodiments. It should be understood thatthese embodiments are only for illustrating the present disclosure anddo not limit the scope of the present disclosure.

The structure and performance of the battery proposed in the embodimentsof the present disclosure will be described in detail below.

The embodiments of the present disclosure relate to a battery includinga positive electrode, a separator, a negative electrode, and anelectrolyte.

The positive electrode plate includes a positive electrode collector anda positive active material layer. The positive current collector in thebattery of the embodiments of the present disclosure will be describedin detail below.

The positive current collector in the battery of the embodiments of thepresent disclosure includes an insulation layer and a conductive layer.The insulation layer is used to support the conductive layer and theconductive layer is used to support the positive active material layerand located above at least one surface of the insulation layer. Theconductive layer has a thickness of D2 which satisfies: 300 nm≤D2≤2 μm.

The conductive layer in the positive current collector used in theembodiments of the present disclosure, on one hand, can meet therequirement that the current collector provides electrons for theelectrode active material layer and thus have a function of conductingand collecting current, thereby improving mechanical strength of thecurrent collector as a whole. On the other hand, the conductive layerhas a thickness of D2 which satisfies: 300 nm≤D2≤2 μm.

The internal resistance of the battery usually includes an ohmicinternal resistance of the battery and a polarization internalresistance of the battery. An active material resistance, a currentcollector resistance, an interface resistance, an electrolytecomposition and the like may all have a significant influence on theinternal resistance of the battery. When a short circuit occurs underabnormal conditions, the internal resistance of the battery may begreatly reduced due to the occurrence of an internal short circuit.Therefore, increasing the resistance of the current collector canincrease the internal resistance of the battery after the short circuit,thereby improving safety performance of the battery. In existing lithiumion batteries, when an internal short circuit occurs in the batteryunder abnormal conditions, a large current would be instantaneouslygenerated, and a large quantity of heat is generated by the shortcircuit accordingly. The heat may usually further initiatealuminothermal reaction at the positive current collector made ofaluminum foil, which may further cause the battery to fire, explode,etc.

In the embodiments of the present disclosure, the above technicalproblems are solved by using a special current collector in which aninsulation layer is used to support and a conductive layer with aspecific thickness is included. In the positive current collector of theembodiment of the present disclosure, the insulation layer isnon-conductive, so its resistance is large. This can improve the shortcircuit resistance of the battery when the short circuit occurs underabnormal conditions, such that the short circuit current can be greatlyreduced, and thus the heat generated by the short circuit can be greatlyreduced, thereby improving the safety performance of the battery.Meanwhile, the specific thickness in the present disclosure can furtherallow the current collector to have a larger resistance. When theconductive layer is made of aluminum, the aluminothermal reaction of thepositive current collector can also be significantly reduced, whichsignificantly reduces temperature rise of the battery during theinternal short circuit, thereby leading to a good safety performance forthe battery.

In some embodiments, the material of the insulation layer is selectedfrom organic polymer insulation materials. The organic polymer has alower density and a lighter weight than metal, and therefore the batterycan be further allowed to have a higher weight energy density. Inaddition, the conductive layer uses the metal layer having a smallerthickness so that the weight energy density of the battery can befurther increased. In addition, since the insulation layer can wellsupport and protect the conductive layer arranged on the surfacethereof, a breakage of the electrode plate, which is common in theconventional current collector, is unlikely to occur.

The organic polymer insulation material is selected from a groupconsisting of polyamide (abbreviated as PA), polyethylene terephthalate(abbreviated as PET), polyimide (abbreviated as PI), and polyethylene(abbreviated as PE), polypropylene (abbreviated as PP), polystyrene(abbreviated as PS), polyvinyl chloride (abbreviated as PVC),acrylonitrile butadiene styrene copolymers (abbreviated as ABS),polybutylene terephthalate (abbreviated as PBT), poly-p-phenyleneterephthamide (abbreviated as PPA), epoxy resin, ethylene propylenerubber (abbreviated as PPE), polyformaldehyde (abbreviated as POM),phenol-formaldehyde resin, polytetrafluoroethylene (abbreviated asPTFE), silicone rubber, polyvinylidene fluoride (abbreviated as PVDF),polycarbonate (abbreviated as PC), or a combinations thereof.

In the current collector according to the embodiments of the presentdisclosure, the insulation layer mainly plays a role of supporting andprotecting the conductive layer. The thickness of the insulation layeris D1, and D1 satisfies 1 μm≤D1≤20 μm. If the insulation layer is toothin, it is likely to be broken during the processing process of theelectrode plate or the like. If the insulation layer is too thick, avolume energy density of the battery adopting the current collector canbe reduced.

An upper limit of the thickness D1 of the insulation layer can be 20 μm,15 μm, 12 μm, 10 μm, or 8 μm, and a lower limit of the thickness D1 ofthe conductive layer can be 1 μm, 1.5 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm,or 7 μm. The thickness D1 of the insulation layer can be in a rangeconsisting of any one upper limit and any one lower limit. Preferably 2μm≤D1≤10 μm, and more preferably 2 μm≤D1≤6 μm.

If the conductive layer is too thin, although it is beneficial toincrease the room temperature thin film resistor R_(S) of the currentcollector, it is easily damaged during processing process of theelectrode plate or the like. If the conductive layer is too thick, itmay affect the weight energy density of the battery, and may not beconductive to increasing the room temperature thin film resistor R_(S)of the conductive layer.

An upper limit of the thickness D2 of the conductive layer can be 2 μm,1.8 μm, 1.5 μm, 1.2 μm, 1 μm, 900 nm, 800 nm, 700 nm, 600 nm, or 500 nm,and a lower limit of the thickness D2 of the conductive layer can be 300nm, 350 nm, 400 nm, or 450 nm. The thickness D2 of the conductive layercan be in a range consisting of any one upper limit and any one lowerlimit. Preferably, 500 nm≤D2≤1.5 μm.

In some embodiments, the material of the conductive layer is selectedfrom metallic conductive materials, and preferably selected from atleast one of aluminum, copper, nickel, titanium, silver, nickel-copperalloy, or aluminum-zirconium alloy.

Further, the conductive layer is preferably made of metallic aluminum.The aluminum content in the conventional positive current collector ishigh, so when a short circuit occurs in the battery under the abnormalconditions, the heat generated at the short circuit point can initiate aviolent aluminothermal reaction, thereby generating a large amount ofheat and causing the explosion or other accidents of the battery. Whenthe battery of the present disclosure is used, since the content ofaluminum in the positive current collector is greatly reduced, thealuminothermal reaction can be avoided, thereby significantly improvingsafety performance of the battery.

The conductive layer can be formed on the insulation layer by means ofat least one of mechanical rolling, bonding, vapor deposition, andelectroless plating. The vapor deposition is preferably physical vapordeposition (PVD). Preferably, the physical vapor deposition is at leastone of evaporation deposition and sputtering deposition. The evaporationdeposition is preferably at least one of vacuum evaporation, thermalevaporation deposition, or electron beam evaporation method (EBEM). Thesputtering deposition is preferably magnetron sputtering.

In the embodiments of the present disclosure, the positive currentcollector further includes a protective layer arranged on at least onesurface of the conductive layer. The protective layer can improve themechanical strength of the conductive layer, further improve the safetyperformance of the battery, and at the same time effectively prevent theconductive layer from being damaged, oxidized or corroded, etc., andsignificantly improve an operating stability and a service life of thecurrent collector.

In the embodiments of the present disclosure, the material of theprotective layer is selected from metal oxides, and preferably selectedfrom at least one of aluminum oxide, cobalt oxide, chromium oxide, andnickel oxide.

The thickness of the protective layer is D3, and D3 satisfies: D3≤ 1/10D2 and 1 nm≤D3≤200 nm, and preferably 10 nm≤D3≤50 nm.

An upper limit of the thickness D3 of the protective layer can be 200nm, 180 nm, 150 nm, 120 nm, 100 nm, 80 nm, 60 nm, 55 nm, 50 nm, 45 nm,40 nm, 30 nm, or 20 nm. A lower limit of the thickness D3 of theprotective layer can be 1 nm, 2 nm, 5 nm, 8 nm, 10 nm, 12 nm, 15 nm, or18 nm. The thickness D3 of the protective layer can be in a rangeconsisting of any one upper limit and any one lower limit. Preferably,10 nm≤D3≤50 nm. If the protective layer is too thin, it is not enough toprotect the conductive layer; and if the protective layer is too thick,the weight energy density and volume energy density of the battery canbe reduced.

From the viewpoint of an accounting proportion of the protective layerin the entire thickness of the conductive layer, D3 satisfies: 1/2000D2≤D3≤ 1/10 D2, that is, the thickness of the protective layer is 1/2000to 1/10 of D2, and more preferably, D3 satisfies: 1/1000 D2≤D3≤ 1/10 D2.

In some embodiments, the protective layer can be arranged on the surfaceof the conductive layer facing away from the insulation layer. In theembodiments of the present disclosure, for convenience of description,when the protective layer is arranged on the surface of the conductivelayer facing away from the insulation layer, i.e., the upper surface ofthe conductive layer, it may be referred to as an upper protectivelayer.

The thickness of the upper protection layer is D3′, and D3′ satisfies:D3′≤ 1/10 D2 and 1 nm≤D3′≤200 nm, i.e., the thickness of the upperprotection layer is smaller than or equal to 1/10 of the thickness D2and is in a range of 1 nm to 200 nm.

When the upper protective layer is made of a metal oxide, the upperprotective layer has a large resistance, so such protective layer canfurther increase the resistance of the positive current collector tosome extent, thereby further improving the short circuit resistance ofthe battery when a short circuit occurs under abnormal conditions andthus improving safety performance of the battery. Secondly, since themetal oxide has low ductility and high hardness, the upper protectivelayer can further increase the mechanical strength of the positivecurrent collector. Thirdly, the specific surface area of the metal oxideis larger than that of the metal, such that a bonding force between theprotective layer made of the metal oxide material and the conductivelayer is stronger, and the protective layer can better protect theconductive layer. Moreover, the bonding force between the protectivelayer having a larger specific surface area and the positive activematerial layer can be further increased. Therefore, compared with thecurrent collector having no protective layer arranged thereon or havingthe upper protective layer made of metal, the current collectoraccording to the embodiments of the present disclosure can furtherincrease the bonding force with the positive active material layer, thusthe overall strength of the battery can be improved.

In some embodiments, the protective layer can also be arranged on thesurface of the conductive layer facing the insulation layer. When theprotective layer is arranged on the surface of the conductive layerfacing the insulation layer, i.e., the lower surface of the conductivelayer, it may be referred to as a lower protective layer.

The lower protective layer can form a complete support structure toprotect the conductive layer, so as to better protect the conductivelayer, thereby preventing the conductive layer from being oxidized,corroded or damaged. In addition, the mechanical strength of the currentcollector is further enhanced. The lower protective layer of the metaloxide material has a large resistance, therefore this type of protectivelayer can further increase the resistance of the positive currentcollector to some extent, thereby further improving the short circuitresistance when the short circuit occurs in the battery under theabnormal conditions, and improving safety performance of the battery. Inaddition, since the specific surface area of the metal oxide is larger,a bonding force between the protective layer made of the metal oxide andthe insulation layer is enhanced. Meanwhile, since the specific surfacearea of the metal oxide is larger, the protective layer can increaseroughness of the surface of the insulation layer, which has a functionof enhancing the bonding force between the conductive layer and theinsulation layer, such that the overall strength of the currentcollector can be enhanced.

The thickness of the lower protective layer is D3″, and D3″ satisfies:D3″≤ 1/10 D2 and 1 nm≤D3″≤200 nm, i.e., the thickness of the lowerprotective layer is smaller than or equal to 1/10 of the thickness D2and is in a range of 1 nm to 200 nm.

In some embodiments, the protective layer can be arranged on the twoopposite surfaces of the conductive layer, that is, both the upperprotective layer and the lower protective layer are arranged.

In some embodiments, when both the upper protective layer and the lowerprotective layer are arranged, a proportional relationship between thethickness D3″ of the lower protective layer and the thickness D3′ of theupper protective layer is: ½ D3′≤D3″≤⅘ D3′. That is, the thickness ofthe upper protective layer is greater than the thickness of the lowerprotective layer. If the thickness of the lower protective layer isincreased, it has little effect on improving the mechanical strength,safety performance, and the like of the current collector, but it canaffect the weight energy density of the battery.

In the battery according to an embodiment of the present disclosure, thematerial of the conductive layer is aluminum, the thickness of theconductive layer is 500 nm≤D2≤1.5 m, the material of the protectionlayer is nickel oxide or aluminum oxide, and the protection layer isarranged on two opposite surfaces of the conductive layer.

FIGS. 1 to 4 are structural schematic diagrams of positive currentcollectors according to embodiments of the present disclosure.

In FIG. 1, the positive current collector 10 includes a positiveinsulation layer 101 and two positive conductive layers 102 providedabove two opposite surfaces of the positive insulation layer 101. Apositive protective layer 103, which is also referred as to an upperprotective layer, is arranged on a surface of each positive conductivelayer 102 facing away from the positive insulation layer 101.

In FIG. 2, the positive current collector 10 includes a positiveinsulation layer 101 and two positive conductive layers 102 arranged ontwo opposite surfaces of the positive insulation layer 101. Two positiveelectrode protective layers 103 are arranged on two opposite surfaces ofeach positive conductive layer 102.

In FIG. 3, the positive current collector 10 includes a positiveinsulation layer 101 and a positive conductive layer 102 arranged on onesurface of the positive insulation layer 101. A positive protectivelayer 103, which is also referred as to an upper protective layer, isarranged on a surface of the positive conductive layer 102 facing awayfrom the positive insulation layer 101.

In FIG. 4, the positive current collector 10 includes a positiveinsulation layer 101 and a positive conductive layer 102 arranged on onesurface of the positive insulation layer. Two positive protective layers103 are arranged on two opposite surfaces of the positive conductivelayer 102.

FIGS. 5 and 6 are structural schematic diagrams of a positive electrodeplate according to embodiments of the present disclosure. As shown inFIGS. 5 and 6, the positive electrode plate 1 includes a positivecurrent collector 10 and a positive active material layer 11 formed on asurface of the positive current collector 10. The positive currentcollector 10 includes a positive insulation layer 101 and one or twopositive conductive layers 102 arranged in this order. There is onepositive electrode protective layer 103 (not shown) arranged on one sideof each positive conductive layer 102, or there are two positiveelectrode protective layers 103 (not shown) arranged on two sides ofeach positive conductive layer 102.

In the positive electrode plate, the positive active material layerincludes a positive active material, a binder, and a conductiveadditive. Since the positive current collector has poorer conductivitythan the conventional aluminum foil current collector, it is preferablethat the mass percentage of the conductive additive is not smaller than0.8 wt % based on a total weight of the positive active material layer.This can ensure that the polarization of the positive electrode plate issmall such that it has small affection on the high rate performance ofthe battery. The higher the content of the conductive additive is, thesmaller the polarization is and the better the rate performance of thebattery will be. However, if the content of the conductive additive istoo high, the charge and discharge capacity of the battery can bereduced. Therefore, it is preferable that the mass percentage of theconductive additive is 0.8 wt % to 2 wt %. Within this preferable range,the upper limit of adding the conductive additive can be 2 wt %, 1.8 wt%, 1.5 wt %, 1.3 wt %, or 1.2 wt %, and the lower limit of adding theconductive additive can be 0.8 wt %, 0.9 wt %, 0.95 wt %, 1.0 wt %, or1.1 wt %.

In some embodiments, the conductive additive can be selected from commonconductive agents for the electrode plate, such as conductive carbonblack, graphene, carbon nanotube, KETJEN black, flake graphite, and thelike.

In some embodiments of the present disclosure, the negative electrodeplate of the battery includes a negative current collector and anegative active material layer. The negative current collector in thebattery according to the embodiments of the present disclosure will bedescribed in detail below.

The negative current collector of the battery according to theembodiments of the present disclosure uses a copper foil currentcollector having a thickness of 6 μm to 12 μm. In order to furtherincrease the weight energy density of the entire battery, it ispreferred to use a copper foil current collector having a thickness of1.0 μm to 5.9 μm. This is because the positive current collector of thebattery according to the present disclosure can improve safetyperformance of the battery, but its conductivity is inferior to that ofthe conventional aluminum foil current collector. Therefore, thisembodiment of the present disclosure uses the copper foil currentcollector of the specific thickness along with the positive currentcollector. The negative current collector according to the embodimentsof the present disclosure has good conductivity and a polarization ofthe electrode plate is small, such that the rate performance of thebattery can be ensured and the negative electrode can be prevented fromprecipitating lithium.

Although selecting a copper foil current collector having a smallerthickness facilitates improving the weight energy density of thebattery, in order to make the battery have both superior electrochemicalperformance and processability, preferably, the negative currentcollector is a copper foil current collector having a thickness of 2.0μm to 5.9 μm, more preferably a copper foil current collector having athickness of 3.0 μm to 5.9 μm, and even more preferably, a copper foilcurrent collector having a thickness of 4.5 μm to 5.9 μm.

In the production process of applying the copper foil current collector,especially a thin copper foil current collector, to the battery product,it is preferable to use a copper foil current collector having anelongation at break greater than or equal to 1%. If the copper foilcurrent collector has an elongation at break smaller than 1%, it isliable to be cracked or broken during processing and battery operation,thereby affecting the cost and long-term reliability of the battery.Preferably, a copper foil current collector having an elongation atbreak greater than or equal to 2% may be used. More preferably, a copperfoil current collector having an elongation at break greater than orequal to 3% may be used.

Further, the copper foil current collector has an elongation at breakgreater than or equal to 1% both in the MD direction and the TDdirection, so that the copper foil current collector has a certainmechanical strength while improving the weight energy density of thebattery. It can be ensured that the copper foil has a good processingproperty during a manufacturing process of the battery. Also, thebattery has good electrochemical properties and long-term reliabilityafter the copper foil is applied to the battery. Preferably, a copperfoil current collector having an elongation at break greater than orequal to 2% both in the MD direction and the TD direction is used. Morepreferably, a copper foil current collector having an elongation atbreak greater than or equal to 3% both in the MD direction and the TDdirection is used.

In the present disclosure, the “length direction (MD direction)” and“width direction (TD direction)” of the copper foil current collectorrefer to two dimensions of a surface, respectively, in which the lengthdirection refers to a main dimension direction (i.e., a direction havinga larger size), and the width direction refers to a secondary dimensiondirection (i.e., a direction having a smaller size). Generally, thelength direction is consistent with a coating direction of respectivematerial layers (e.g., the electrode active material layer) during amanufacturing process of an electrode plate, and is also consistent witha winding direction of the electrode plate during a manufacturingprocess of an electrochemical device (e.g., a battery). The widthdirection is perpendicular to the length direction.

In the present disclosure, the copper foil current collector may be acurrent collector made of a metallic copper, or may be a currentcollector of a copper alloy such as a copper-nickel alloy, acopper-chromium alloy, a copper-zinc alloy, red copper, bronze, or thelike. Preferably, the content of the copper element in the copper alloyis 90% by weight or more.

Further, the battery of the present disclosure is preferably a negativeelectrode plate having a following overcurrent capacity: a single pieceof the negative electrode plate having a width of 50 mm, and a fusingtime of 10 s or more at a current of 10 A. This is because when a thincopper foil current collector is used as the current collector, thenegative electrode plate is also required to have a certain overcurrentcapacity, otherwise it is easy to “blow” during an operation of thebattery, thereby affecting the electrochemical performance and normaloperation of the battery.

The test method for the overcurrent capacity of the negative electrodeplate is as follows. The negative electrode plate was cut to a sizeshown in FIG. 10, and a current of 10 A was applied to observe thefusing time. The shorter the fusing time is, the worse its overcurrentcapacity is.

It should be noted here that the elongation at break of the copper foilcurrent collector is related to defects in the current collector, whichare then related to the process of forming the current collector and itscomposition. Generally, the thinner the thickness of the copper foilcurrent collector is, the more difficult the processing is and the moredefects there are. This may also directly affect the overcurrentcapacity of the negative electrode plate containing the copper foilcurrent collector. Therefore, in order to make the battery have bothhigh weight energy density and excellent electrochemical performance, itis necessary to use a thin copper foil current collector that has alarge elongation at break and may lead to a good overcurrent capacityfor the negative electrode plate.

In the battery according to the embodiments of the present disclosure,an electrolyte is further included. As an improvement in the embodimentsof the present disclosure, in order to further improve the high rateperformance of the battery, the room temperature conductivity of theelectrolyte is 6.0 mS/cm to 9.0 mS/cm, which can further ensure thatlithium is not precipitated from the negative electrode. The higher theroom temperature conductivity of the electrolyte is, the better the rateperformance of the battery is. However, if increasing the content of acertain type of organic solvent is merely for increasing the roomtemperature conductivity, the side reaction can be increased because theadding proportion of certain organic solvent is too large, and it mayaffect a cycle life of the battery to some extent.

If the room temperature conductivity of the electrolyte is too high, inan embodiment of the electrolyte, for example, the room temperatureconductivity of the electrolyte can be adjusted by adjusting theproportion of the cyclic carbonate and the chain carbonate. If the roomtemperature conductivity is too high, it is needed to increase theaddition amount of the cyclic carbonate, which may increase the sidereaction. In addition, the room temperature conductivity can also beimproved by adding carboxylic acid ester, and it is not limited to thismanner.

According to the winding method, the battery according to theembodiments of the present disclosure can be of a wound type or alaminated type. The battery can also be one of a lithium ion secondarybattery, a primary lithium battery, a sodium ion battery, and amagnesium ion battery. However, it is not limited to these batteries.

In the embodiments of the present disclosure, a nailing experiment isused to simulate the abnormal conditions of the battery and observe achange of the battery after nailing. FIG. 7 is a schematic diagram of aone-time nailing experiment of the present disclosure. For the sake ofsimplicity, the drawing merely shows that a nail 4 punctures one layerof positive electrode plate 1, one layer of separator 3 and one layer ofnegative electrode plate 2 of the battery. It should be noted that thenail 4 penetrates the entire battery in the actual nailing experiment.The entire battery generally includes a plurality of layers of positiveelectrode plate 1, separator 3, and negative electrode plate 2. When ashort circuit occurs in the battery due to the nailing, the shortcircuit current is greatly reduced, and the heat generated during theshort circuit is controlled within a range that the battery can fullyabsorb. Therefore, the heat generated at the position where the internalshort circuit occurs can be completely absorbed by the battery, and thetemperature rise of the battery is also very small, such that the damageon the battery caused by the short circuit can be limited to the nailingposition, and only a “point break” can be formed without affecting thenormal operation of the battery in a short time.

Embodiment 1

1. Preparation of Positive Current Collector

An insulation layer having a certain thickness is selected, and aconductive layer having a certain thickness is formed on the surface ofthe insulation layer by means of vacuum evaporation, mechanical rollingor bonding, and the protective layer is formed by means of vapordeposition, in-situ formation or coating.

1.1 Formation of Conductive Layer

There are several manners to form the conductive layer as follows.

(1) The conditions of the vacuum evaporation for forming the conductivelayer are as follows: the insulation layer is placed in a vacuumevaporation chamber after a surface cleaning treatment, a high-puritymetal wire in a metal evaporation chamber is melted and evaporated at ahigh temperature in a range of 1600° C. to 2000° C., the evaporatedmetal passes through a cooling system in the vacuum evaporation chamberand is finally deposited on the surface of the insulation layer to formthe conductive layer.

(2) The conditions of the mechanical rolling for forming the conductivelayer are as follows: a foil of a material used for the conductive layeris placed in a mechanical roller, rolled to a predetermined thickness byapplying a pressure in a range of 20 t to 40 t, and then placed on asurface of the insulation layer that has been subjected to a surfacecleaning treatment, and finally the both are placed in the mechanicalroller, so as to be tightly bonded by applying a pressure in a range of30 t to 50 t.

(3) The conditions of the bonding for forming the conductive layer areas follows: a foil of a material used for the conductive layer is placedin a mechanical roller, rolled to a predetermined thickness by applyinga pressure in a range of 20 t to 40 t, and then a mixed solution of PVDFand NMP is applied on a surface of the insulation layer that has beensubjected to a surface cleaning treatment, and finally the conductivelayer having the above predetermined thickness is bonded to the surfaceof the insulation layer and dried at 100° C.

1.2 Formation of Protective Layer

There are several manners to form a protective layer as follows.

(1) A protective layer is firstly arranged on a surface of theinsulation layer by means of vapor deposition or coating, and then aconductive layer having a certain thickness is formed on the protectivelayer disposed on the insulation layer by means of vacuum evaporation,mechanical rolling or bonding, so as to prepare a current collectorhaving a lower protective layer (the protective layer is located betweenthe insulation layer and the conductive layer). In addition,alternatively, on the basis of the above, an upper protective layer isfurther formed on a surface of the conductive layer facing away from theinsulation layer by means of vapor deposition, in-situ formation orcoating, so as to prepare a current collector having an upper protectivelayer and a lower protective layer (which are located on two oppositesurfaces of the conductive layer).

(2) A protective layer is firstly formed on a surface of the conductivelayer by means of vapor deposition, in-situ formation, or coating, andthen the conductive layer provided with the above protective layer isarranged on a surface of the insulation layer by means of mechanicalrolling or bonding, and the protective layer is arranged between theinsulation layer and the conductive layer, so as to prepare a currentcollector having a lower protective layer (the protective layer islocated between the insulation layer and the conductive layer). Inaddition, alternatively, on the basis of the above, an upper protectivelayer is further formed on a surface of the conductive layer facing awayfrom the insulation layer by means of vapor deposition method, in-situformation, or coating, so as to prepare a current collector having anupper protective layer and a lower protective layer (which are locatedon two opposite surfaces of the conductive layer);

(3) A protective layer is firstly formed on a surface of the conductivelayer by means of vapor deposition, in-situ formation, or coating, andthen the conductive layer provided with the above protective layer isarranged on a surface of the insulation layer by means of mechanicalrolling or bonding, and the protective layer is arranged on a surface ofthe conductive layer facing away from the insulation layer, so as toprepare a current collector having an upper protective layer (which islocated on the surface of the conductive layer facing away from theinsulation layer);

(4) A protective layer is firstly formed on two surfaces of theconductive layer by means of vapor deposition, in-situ formation, orcoating, and then the conductive layer provided with the aboveprotective layer is arranged on the surface of the insulation layer bymeans of mechanical rolling or bonding, so as to prepare a currentcollector having an upper protective layer and a lower protective layer(which are located on two opposite surfaces of the conductive layer);

(5) A conductive layer is formed on the surface of an insulation layer,and then an upper protective layer is formed on the surface of theconductive layer facing away from the insulation layer by means of vapordeposition, in-situ formation, or coating, so as to prepare a currentcollector having an upper protective layer (which is located on thesurface of the conductive layer facing away from the insulation layer).

In the embodiments of preparation, the vapor deposition is vacuumevaporation, the in-situ formation is in-situ passivation, and thecoating is blade coating.

The conditions of the vacuum evaporation for forming the protectivelayer are as follows: a sample is placed in a vacuum evaporation chamberafter a surface cleaning treatment, a material of the protective layerin the evaporation chamber is melted and evaporated at a hightemperature in a range of 1600° C. to 2000° C., and the evaporatedmaterial of the protective layer passes through a cooling system in thevacuum evaporation chamber and is finally deposited on a surface of thesample, so as to form the protective layer.

The conditions of the in-situ passivation are as follows: the conductivelayer is placed in a high-temperature oxidizing environment, thetemperature is controlled within a range of 160° C. to 250° C., and theoxygen supply is maintained in the high-temperature environment, andprocessing time is 30 min, so as to form a protective layer of metaloxide.

The conditions of the gravure coating are as follows: a material of theprotective layer and NMP are stirred and mixed, then the slurry of theabove material of the protective layer (solid material content is 20% to75%) is coated on a surface of the sample, the thickness of the coatingis controlled by a gravure roll, and finally the coating is dried at 100to 130° C.

2. Negative Current Collector

A copper foil having a thickness of 8 μm is selected as a negativeelectrode collector (i.e., negative electrode plate 1#).

3. Preparation of Electrode Plate:

The positive electrode slurry or the negative electrode slurry is coatedon a surface of the current collector by a conventional coating processof battery and dried at 100° C., so as to obtain a positive electrodeplate or negative electrode plate. Here, the mass percentage of theconductive additive (conductive carbon black) is not smaller than 0.8 wt% based on the total weight of the positive active material layer.

Specific parameters of the prepared positive electrode plate are shownin Tables 1 and 2. In Table 2, Positive Electrode Plate 1-1 representsan electrode plate obtained by preparing a corresponding protectivelayer on Positive Electrode Plate 1, and so on.

The current collector of the conventional positive electrode plate is anAl foil having a thickness of 12 μm, the positive active material layeris a ternary (NCM) material layer of 55 μm, and the mass percentage ofthe conductive additive is 1.5 wt %.

Negative electrode plate: The negative current collector is a Cu foilhaving a certain thickness, and the negative active material layer is agraphite material layer of 55 μm.

4. Preparation of Electrolyte

Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are used asorganic solvents (EC: EMC in a volume ratio of 1:10 to 10:1); theelectrolyte is LiPF₆ and the concentration of LiPF₆ is 1 mol/L.

By adjusting the volume ratio of EC and EMC, electrolytes having a roomtemperature conductivity of 6.5 mS/cm, 7.0 mS/cm, 7.3 mS/cm, 8.0 mS/cm,8.5 mS/cm, or 9.0 mS/cm are prepared respectively for the preparation ofthe battery.

5. Preparation of the Battery:

A positive electrode plate, a PP/PE/PP separator and a negativeelectrode plate are wound together to form a bare cell by a conventionalbattery manufacturing process, then the bare cell is placed into abattery case, an electrolyte is injected into the case, followed bysealing, formation, and the like, so as to obtain a lithium ion battery.The standard battery capacity (25° C., 1 C/1 C) is 3.2 Ah.

Specific compositions of the lithium ion battery prepared in theembodiments of the present disclosure and the batteries of thecomparative examples are shown in Table 3.

TABLE 2 Positive current collector Positive active Conductive Electrodeactive material layer Electrode Insulation layer layer material layerContent of plate No. Material D1 Material D2 Material Thickness theconductive agent Positive PI  2 μm Al  800 nm NCM 55 μm 1.5 wt %electrode plate     1#     Positive PI  5 μm Al   2 μm NCM 55 μm 1.5 wt% electrode     plate     2#     Positive PI  6 μm Al  300 nm NCM 55 μm1.5 wt % electrode plate     3#     Positive PET  5 μm Al  500 nm LCO 55μm 1.3 wt % electrode   plate   4#   Positive PET 10 μm Al   1 μm NCM 55μm 1.2 wt % electrode plate 5# Positive PET  8 μm Ni  1.5 μm LCO 55 μm0.8 wt % electrode plate 6#

TABLE 2 Lower protective layer Upper protective layer Electrode plateNo. Material D3″ Material D3′ Positive / / nickel oxide  1 nm electrodeplate 1-1# Positive / / nickel oxide 10 nm electrode plate 1-2# Positive/ / aluminum 50 nm electrode plate oxide 1-3# Positive / / nickel oxide200 nm  electrode plate 2-4# Positive nickel oxide  5 nm nickel oxide 10nm electrode plate 1-5# Positive nickel oxide  8 nm nickel oxide 10 nmelectrode plate 1-6# Positive nickel oxide 20 nm nickel oxide 50 nmelectrode plate 1-7# Positive nickel oxide 30 nm nickel oxide 50 nmelectrode plate 2-8# Positive nickel oxide 50 nm nickel oxide 100 nm electrode plate 2-9# Positive aluminum 100 nm  nickel oxide 200 nm electrode plate oxide 2-10# The symbol “/” indicates that no protectivelayer is arranged.

TABLE 3 Electrolyte Room temperature electric conductivity Battery No.Composition of the electrode plate (mS/cm) Battery 1# ConventionalNegative electrode 6.5 positive electrode plate 1# plate Battery 2#Positive electrode Negative electrode 7.0 plate 1# plate 1# Battery 3#Positive electrode Negative electrode 8.0 plate 2# plate 1# Battery 4#Positive electrode Negative electrode 6.0 plate 1-1# plate 1# Battery 5#Positive electrode Negative electrode 8.0 plate 1-2# plate 1# Battery 6#Positive electrode Negative electrode 7.0 plate 1-3# plate 1# Battery 7#Positive electrode Negative electrode 8.0 plate 2-4# plate 1# Battery 8#Positive electrode Negative electrode 8.0 plate 1-5# plate 1# Battery 9#Positive electrode Negative electrode 8.5 plate 1-6# plate 1# Battery10# Positive electrode Negative electrode 8.0 plate 1-7# plate 1#Battery 11# Positive electrode Negative electrode 7.3 plate 2-8# plate1# Battery 12# Positive electrode Negative electrode 8.0 plate 2-9#plate 1# Battery 13# Positive electrode Negative electrode 9.0 plate2-10# plate 1#Experimental 2

1. Test Method of the Batteries:

A method for testing cycle life of the lithium ion battery was performedas follows.

A lithium ion battery was charged and discharged at 25° C. and 45° C.respectively, that is, it was firstly charged with a current of 1 C to avoltage of 4.2V, then discharged with a current of 1 C to a voltage of2.8V, and the discharge capacity after a first cycle was recorded; andthe battery was subjected to 1000 cycles of 1 C/1 Ccharging-discharging, and the discharge capacity of the battery after a1000^(th) cycle was recorded. A capacity retention rate after the1000^(th) cycle was obtained by dividing the discharge capacity afterthe 1000^(th) cycle by the discharge capacity after the first cycle.

The experimental results are shown in Table 4.

2. Test Methods of One-Time Nailing Experiment and Six ConsecutiveNailing Experiment:

(1) One-time nailing experiment: a battery that had been fully chargedwas fixed, a steel needle with a diameter of 8 mm penetrates puncturedthrough the battery at a speed of 25 mm/s at room temperature andremained in the battery, and the battery was observed and measured afterthe nailing was finished.

(2) Six-time nailing experiment: a battery that had been fully chargedwas fixed, six steel needles with a diameter of 8 mm rapidly puncturedthrough the battery successively at a speed of 25 mm/s at roomtemperature and remained in the battery, and the battery was observedand measured after the nailing was finished.

(3) Measurement of battery temperature: a multichannel thermometer wasused, and the temperature-sensing wires were respectively attached ongeometric centers of a nail-inserting surface and an opposite surface ofthe battery to be nailed; after the nailing was finished, temperature ofthe battery was measured and tracked for 5 minutes, and the temperatureof the battery at the end of the 5 minutes was recorded.

(4) Measurement of battery voltage: positive and negative electrodes ofeach battery to be nailed were connected to test terminals of aninternal resistance instrument; after the nailing was finished, avoltage of each battery was measured and tracked for 5 minutes, and thevoltage of the battery at the end of 5 minutes was recorded.

The data of the recorded battery temperatures and voltages are shown inTable 5.

3. Rate Experiment

A rate experiment was performed for the lithium ion battery. Thespecific test method was performed as follows.

The lithium ion battery was charged and discharged at 25° C., i.e., thebattery was firstly charged with a current of 1 C to a voltage of 4.2V,and then was discharged with a current of 1 C to a voltage of 2.8V. Thedischarge capacity after the first cycle was recorded and divided by thedischarge capacity at 25° C. with 1 C/1 C charge-discharge after thefirst cycle to obtain a 4 C rate performance of the battery.

The experimental results are shown in Table 6.

TABLE 4 Capacity retention ratio after the 1000^(th) cycle (1 C/1 C)Battery No. 25° C. 45° C. Battery 1# 89.2% 86.5% Battery 2# 86.5% 80.7%Battery 3# 86.8% 80.8% Battery 4# 87.7% 81.9% Battery 5# 88.2% 83.2%Battery 6# 88.7% 86.2% Battery 7# 88.9% 86.0% Battery 8# 88.2% 82.8%Battery 9# 88.5% 85.2% Battery 10# 88.7% 85.3% Battery 11# 88.6% 85.7%Battery 12# 88.9% 86.2% Battery 13# 89.1% 86.1%

TABLE 5 One-time Six-time consecutive nailing nailing experimentexperiment Battery Battery Battery Battery temperature rise voltagetemperature rise voltage Battery No. (° C.) (V) (° C.) (V) Battery 1#500 0 N/A N/A Battery 2# 13.2 3.82 15.4 3.95 Battery 3# 15.2 3.85 15.73.84 Battery 4# 5.4 4.12 3.6 4.08 Battery 5# 4.9 4.14 3.4 4.08 Battery6# 4.3 4.11 3.4 4.09 Battery 7# 4.9 4.05 4.4 4.12 Battery 8# 3.9 4.124.1 4.12 Battery 9# 5.1 4.13 4.0 4.04 Battery 10# 4.4 4.11 3.6 4.05Battery 11# 5.6 4.14 4.5 4.08 Battery 12# 5.1 4.12 4.5 4.09 Battery 13#4.7 4.12 4.1 4.12 Note: “N/A” indicates that thermal runaway and damagehappened immediately after one steel needle punctured through thebattery.

TABLE 6 Battery No. 4 C rate performance Battery 1# 46.0% Battery 2#43.4% Battery 4# 43.3%

The graph of temperature of Battery 1# and Battery 4# with time is shownin FIG. 8, and the graph of voltage with time is shown in FIG. 9.

According to the results in Table 5, compared with Battery 1# using theconventional positive electrode plate and the conventional negativeelectrode plate, the battery according to the embodiments of the presentdisclosure has good cycle performance, which is equivalent to the cycleperformance of the conventional battery. This shows that the currentcollectors according to the embodiments of the present disclosure do nothave any significant adverse effects on the resulting electrode platesand batteries. Compared with a current collector having no protectivelayer, the battery prepared by the current collector provided with theprotective layer can have a further improved capacity retention rate,indicating a better reliability of the battery.

In addition, the battery according to the embodiments of the presentdisclosure can have good safety performance. From the results in Table 6and FIGS. 8 and 9, the battery temperature of Battery 1# (conventionalbattery) at the moment of nailing rose suddenly by hundreds ofcentigrade degree and the voltage thereof suddenly dropped to zero. Thisshows that the internal short circuit occurred in the battery at themoment of nailing, a large amount of heat was generated, a thermalrunaway and damage of the battery instantly occurred, such that thebattery is unable to continue operating. Furthermore, due to the thermalrunaway and damage of the battery occurring immediately after the firststeel needle punctured into the battery, it is impossible to perform thecontinuous nailing on this type of battery by using six steel needles.

With the battery according to the embodiments of the present disclosure,the temperature rise of the battery can basically be controlled under 6°C., the voltages are substantially constant, and the battery can operatenormally, no matter in one-time nailing experiment or in six-timecontinuous nailing experiment. Moreover, the battery provided with aprotective layer made of a metal oxide material can have the bettersafety performance. Thus, in the event of an internal short circuit inthe battery, the battery according to the embodiments of the presentdisclosure can greatly reduce the heat generation caused by the shortcircuit, thereby improving the safety performance of the battery. Inaddition, the damage on the battery caused by the short circuit can belimited to a “point”, and thus merely forms a “point break”, withoutaffecting the normal operation of the battery in a short time.

According to the results in Table 6, using the negative currentcollector within the thickness range of the present disclosure, theconductive additive within the content range of the present disclosureand the electrolyte within the parameters of the present disclosure canachieve good rate performance. The battery according to the embodimentsof the present disclosure has good rate performance comparable to aconventional battery.

Embodiment 3

Different from Example 1, a copper foil having a thickness of 1 μm to 12μm is selected as the negative electrode current collector.

1. Test for Elongation at Break of the Negative Current Collector:

Nine types of negative electrode current collectors with a thicknessesranging from 1 μm to 12 μm were selected, and two negative electrodecurrent collector samples having a length of 200 mm and a width of 15 mmwere taken on a negative current collector. Then, the negative electrodecurrent collector sample was fixed on a tensile machine (Model AI7000),an initial length L0 was recorded, the tensile machine was started untilthe negative electrode current collector sample was broken, and then adisplacement distance L1 of the negative electrode current collectorsample at the time of being broken was read from the tensile machine. Anaverage values obtained from two tests is a test result. The elongationat break=(L1−L0)/L0*100%.

The data on the elongation at break of the negative electrode currentcollector is shown in Table 7.

2. Test for the Overcurrent Capacity of the Negative Current Collector:

Nine types of negative electrode plates having a thickness of 1 μm to 12μm were cut into the sizes as shown in FIG. 10, and a current of 10 Awas applied to observe the fusing time. The data on the fusing time forthe negative current collector is shown in Table 7. It should be notedthat the overcurrent capacity of the electrode plate is related to awidth of the electrode plate after cutting. The influence of the widthof the tab, the length of the electrode plate and the type of activematerial on the overcurrent capacity is negligible. An example is shownin FIG. 10.

3. Preparation of the Battery:

In the conventional battery manufacturing process, the positiveelectrode plates 2-9, the PP/PE/PP separators and the negative electrodeplates 1# to 9# in Embodiment 1 were respectively wound into a barecell, which was then placed into the battery housing. An electrolyte wasthen injected, followed by sealing and chemical conversion and the like,and finally a lithium ion battery was obtained. The standard batterycapacity (25° C., 1 C/1 C) is 3.2 Ah.

The specific compositions of the lithium ion battery and the comparativelithium ion battery manufacture in the present disclosure are shown inTable 8.

4. A method for testing cycle life of the lithium ion battery wasperformed as follows.

A lithium ion battery was charged and discharged at a temperature of 25°C.±2° C., that is, it was firstly charged with a current of 1 C to avoltage of 4.2V, then discharged with a current of 1 C to a voltage of2.8V, and the discharge capacity after a first cycle was recorded; andthe battery was subjected to 1000 cycles of 1 C/1 Ccharging-discharging, and the discharge capacity of the battery after a1000^(th) cycle was recorded. A capacity retention rate after the1000^(th) cycle was obtained by dividing the discharge capacity afterthe 1000^(th) cycle by the discharge capacity after the first cycle.

The experimental results are shown in Table 9.

TABLE 7 Overcurrent capacity Negative current collector of the negativeElongation electrode plate at at break 10 A Electrode plate No. MaterialThickness (%) fusing time (s) Negative electrode Cu 8 μm 6.0 >1000 plate1# Negative electrode Cu 1 μm 1.0 15 plate 2# Negative electrode Cu 2 μm1.5 191 plate 3# Negative electrode Cu 3 μm 2 >1000 plate 4# Negativeelectrode Copper 4 μm 2.1 >1000 plate 5# alloy Negative electrode Cu 4.5μm   2.5 >1000 plate 6# Negative electrode Cu 5.6 μm   3.0 >1000 plate7# Negative electrode Cu 5.9 μm   2.8 >1000 plate 8# Negative electrodeCu 12 μm  6.5 >1000 plate 9#

Among them, the composition of the copper alloy used for the negativeelectrode plate 5# is 95 wt % of copper and 5 wt % of nickel.

TABLE 8 Electrolyte Conductivity at normal temperature Battery No.Composition of electrode plate (mS/cm) Battery 12# Positive electrodeNegative electrode 8.0 plate 2-9# plate 1# Battery 22# Positiveelectrode Negative electrode 8.0 plate 2-9# plate 2# Battery 23#Positive electrode Negative electrode 8.0 plate 2-9# plate 3# Battery24# Positive electrode Negative electrode 8.0 plate 2-9# plate 4#Battery 25# Positive electrode Negative electrode 8.0 plate 2-9# plate5# Battery 26# Positive electrode Negative electrode 8.0 plate 2-9#plate 6# Battery 27# Positive electrode Negative electrode 8.0 plate2-9# plate 7# Battery 28# Positive electrode Negative electrode 8.0plate 2-9# plate 8# Battery 9# Positive electrode Negative electrode 8.0plate 2-9# plate 9#

TABLE 9 Weight energy density Capacity retention ratio (%) after BatteryNo. (wh/kg) the 1000th cycle at 25° C. Battery 12# 248 88.9 Battery 22#264 21.2 Battery 23# 261 29.7 Battery 24# 258 48.3 Battery 25# 257 69.9Battery 26# 257 75.4 Battery 27# 252 90.2 Battery 28# 252 89.7 Battery9# 240 89.9

According to the results in Tables 7-9, the copper foil currentcollector of the negative electrode plates 2# to 8# is thinner than thatof the negative electrode plate 1#, and therefore, the copper foilcurrent collector having the thickness of 1 μm to 5.9 μm can meet therequirements of elongation at break (elongation at break ≥1%), so thatthe copper foil current collector has a certain mechanical strength toensure good processing property of the copper foil during batterymanufacturing.

In the copper foil current collector of the negative electrode plates 2#to 8#, the negative electrode plate 2# and the negative electrode plate3# have a short fusing time and a poor overcurrent capacity. Therefore,the copper foil current collector having a thickness of 2.0 μm to 5.9 μmhas a thin thickness, a large elongation at break, a long fusing time,and a good overcurrent capacity.

In addition, as can be seen from the results of Table 9, the lithium ionbattery formed by the negative electrode plates 2#˜8# has a weightenergy density of 250 wh/kg or higher, and compared to the lithium ionbattery formed by the negative electrode plate 1# or the negativeelectrode plate 9#, it can effectively increase the weight energydensity, and as the thickness of the copper foil current collectorincreases, the cycle stability of the battery is also graduallyimproved.

The preferable embodiments of the present disclosure are disclosed abovebut are not used to limit the claims. Those skilled in the art may makepossible changes and modifications without departing from the concept ofthe present disclosure. Therefore, the protection scope of the presentdisclosure is defined by the attached claims.

What is claimed is:
 1. A battery, comprising a positive electrode plate comprising a positive current collector and a positive active material layer; a negative electrode plate comprising a negative current collector and a negative active material layer, and an electrolyte, wherein the positive current collector comprises an insulation layer and at least one conductive layer, the insulation layer is used to support the at least one conductive layer, each of the at least one conductive layer is used to support the positive active material layer and is located above at least one surface of the insulation layer, and each of the at least one conductive layer has a thickness of D2 satisfying: 300 nm≤D2≤2 μm, wherein at least one protective layer is arranged on at least one surface of each of the at least one conductive layer, and wherein the negative current collector is a copper foil current collector having a thickness of 1 μm to 5.9 μm, the at least one protective layer is made of aluminum oxide, cobalt oxide, chromium oxide, nickel oxide, or combinations thereof, and the at least one protective layer includes a first protective layer arranged on a surface of one of the at least one conductive layer facing the insulation layer, and a second protective layer arranged on a surface of one of the at least one conductive layer facing away from the insulation layer, and a thickness of the second protective layer is greater than a thickness of the first protective layer.
 2. The battery according to claim 1, wherein the at least one conductive layer is made of a metallic conductive material, and the metallic conductive material is selected from a group consisting of aluminum, copper, nickel, titanium, silver, nickel-copper alloy, aluminum-zirconium alloy, or combinations thereof.
 3. The battery according to claim 1, wherein each of the at least one protective layer has a thickness of D3 satisfying: D3≤ 1/10 D2 and 1 nm≤D3≤200 nm.
 4. The battery according to claim 1, wherein the positive active material layer comprises a positive active material, a binder, and a conductive additive, and wherein a mass percentage of the conductive additive to the positive active material layer is larger than or equal to 0.8 wt %.
 5. The battery according to claim 1, wherein the electrolyte has a room temperature conductivity of 6.0 mS/cm to 9.0 mS/cm.
 6. The battery according to claim 1, wherein the at least one conductive layer is made of aluminum, and the thickness of the conductive layer satisfies 500 nm ≤D2 ≤1.5 μm.
 7. The battery according to claim 1, wherein the insulation layer has a thickness of D1 satisfying: 1 μm≤D1≤20 μm; the insulation layer is made of an organic polymer insulation material, and the organic polymer insulation material is selected from a group consisting of polyamide, polyethylene terephthalate, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate, poly-p-phenylene terephthalamide, ethylene propylene rubber, polyformaldehyde, epoxy resin, phenol-formaldehyde resin, polytetrafluoroethylene, polyvinylidene fluoride, silicone rubber, polycarbonate, or combinations thereof.
 8. The battery according to claim 1, wherein the negative current collector is a copper foil current collector having a thickness of 2.0 μm to 5.9 μm.
 9. The battery according to claim 1, wherein an overcurrent capacity of the negative electrode plate includes a fusing time at 10A greater than or equal to 10 seconds for a single piece of the negative electrode plate having a width of 50 mm.
 10. The battery according to claim 1, wherein each of the at least one protective layer has a thickness of D3 satisfying: D3≤ 1/10 D2 and 10 nm≤D3≤50 nm.
 11. The battery according to claim 1, wherein the insulation layer has a thickness of D1 satisfying: 2 μm≤D1≤10 μm, and wherein the insulation layer is made of an organic polymer insulation material, and the organic polymer insulation material is selected from a group consisting of polyamide, polyethylene terephthalate, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate, poly-p-phenylene terephthalamide, ethylene propylene rubber, polyformaldehyde, epoxy resin, phenol-formaldehyde resin, polytetrafluoroethylene, polyvinylidene fluoride, silicone rubber, polycarbonate, or combinations thereof.
 12. The battery according to claim 1, wherein the insulation layer has a thickness of D1 satisfying: 2 μm≤D1≤6 μm, and wherein the insulation layer is made of an organic polymer insulation material, and the organic polymer insulation material is selected from a group consisting of polyamide, polyethylene terephthalate, polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, acrylonitrile-butadiene-styrene copolymer, polybutylene terephthalate, poly-p-phenylene terephthalamide, ethylene propylene rubber, polyformaldehyde, epoxy resin, phenol-formaldehyde resin, polytetrafluoroethylene, polyvinvlidene fluoride, silicone rubber, polycarbonate, or combinations thereof.
 13. The battery according to claim 1, wherein the negative current collector is a copper foil current collector having a thickness of 3.0 μm to 5.9 μm.
 14. The battery according to claim 1, wherein the negative current collector is a copper foil current collector having a thickness of 4.5 μm to 5.9 μm.
 15. The battery according to claim 1, wherein the copper foil current collector has an elongation at break greater than or equal to 1%.
 16. The battery according to claim 1, wherein the copper foil current collector has an elongation at break greater or equal to 2%.
 17. The battery according to claim 1, wherein the copper foil current collector has an elongation at break greater than or equal to 3%.
 18. The battery according to claim 1, wherein both in a MD direction and a TD direction, the copper foil current collector has an elongation at break greater than or equal to 1%.
 19. The battery according to claim 1, wherein both in a MD direction and a TD direction, the copper foil current collector has an elongation at break greater than or equal to 2%.
 20. The battery according to claim 1, wherein both in a MD direction and a TD direction, the copper foil current collector has an elongation at break greater than or equal to 3%. 